1. Field of the Invention
The present invention relates to the field of printing technology, particularly four-color printing. The invention is more particularly concerned with color reduction in four-color printing dependent on tone, whereby the color components of the chromatic printing inks, yellow, magenta and cyan, are reduced and the amount of black printing ink is increased to compensate for this reduction.
2. Description of the Prior Art
As already known from the publication FOGRA-Forschungsbericht 1.203, Untersuchungen zur Veranderung des Farbsatzaufbaues durch geanderte Farbausuuge fur die Teilfarbe Schwarz von Gunter Otschik, at Page 4, right-hand column. Chapter 3.1, it is possible to work with a total reduction of chromatic inks, i.e., achromatic synthesis of the reproduction when an intensive black, i.e. an intensive but expensive printing ink "black", is available.
What is meant by total achromatic synthesis in reproduction technology is that printing is only carried out with black ink in the reproduction of gray tone values and in the extremely dark tones, i.e. that no chromatic color component is contained and printed in the color separations yellow, magenta and cyan in these image areas.
Using less expensive printing inks for the color black ink usually employed in practice, however, a gray cast occurs when 100% black ink is printed. For this reason, the color separations of the chromatic printing inks are not reduced to zero but, rather, a residue of chromatic ink, which leads to a higher density, is printed over the entire tone range in gray tones up to the deepest black shadow, whereby the residual value decreases progressively towards light tones.
Thereby, the danger exists that color casts will occur in the reproduction of gray tones in the entire tonal range when fluctuations occur in the equilibrium i.e. gray balance portions of the chromatic printing inks yellow (Y), magenta (M), and cyan (C), and this can easily occur during the printing process, according to the initially-mentioned FOGRA-Forschungsbericht, pp. 3-4, Chapters 1 and 2.
Another disadvantage in comparison to total achromatic synthesis is that, in case the gray tones are still reproduced by chromatic components, a high ink consumption of the chromatic ink occurs instead of using an intensive black ink.